Make migrations easier when testing in docker

[pingiun]

No description provided.

[joren485]

Could you elaborate on what is not easy at the moment?

[pingiun]

Just like with production_entrypoint.sh we can create the db folder and automatically run migrate and collectstatic. We can check how concrexit is doing this.

[thomwiggers]

Concrexit containers use postgresql, so it does not have to deal with any db folder

[pingiun]

This was partly fixed by #22 although we can still automatically run migrate and collectstatic with an entrypoint script